On the Endpoint Protection Manager server (SEPM) the data\outbox folder contains many subfolders with dax and dax.sig files.
Release : 14.3x
These are delta signature updates for IPS.
Clients requested delta updates can generate these subfolders and signature files. The more versions of the SEP client and platforms supported (Linux, Mac, Windows) are in the environment, the more folders can be contained here.
To minimize, Upgrade clients to the latest version of the SEP Client so multiple versions of definitions are not needed.
Also make sure the default number of definitions is not increased too much. It's found in the console under Admin > Servers > select the site, right-click > Edit > LiveUpdate. Under Disk Space Management for Downloads 90 is the default value.